The metabolism of nucleoside analogues which posses antiviral activity is directly related to therapeutic efficacy and cytotoxicity. The metabolic contributions of both the host and virus play important roles. The specific aims of this research will be to answer important questions concerning the metabolism of antiviral compounds relating to wound healing, chemotherapy, and viral pathogenicity in herpes simplex virus eye infections. The first specific aim will be to determine the distribution of antiviral compounds and their metabolites on ocular tissues following topical therapy. Tritium labeled nucleoside analogues will be topically instilled into the eyes of normal and HSV-1 infected rabbits, the eyes enucleated, fractionated, and the tissue contents quantitatively analyzed by high performance liquid chromatography (HPLC). Simultaneous topical application of nucleoside antivirals and inhibitors of catabolic enzymes to corneas of rabbits will be evaluated in order to determine if "co-therapy" will be an effective approach to increase the efficacy of antiviral compounds. For example, "co-therapy" with 9-Beta-D-arabinofuranysyladenine (ARA-A) and adenosine deaminase inhibitors will be investigated to determine if the conversion of ARA-A to 9-Beta-D-arabinofuranosylhypoxanthine (ARA-Hx) in rabbit eyes can effectively be blocked. Another specific aim will be to determine if selective protection therapy with compounds such as 5'amino-thymidine can protect corneal epithelial and stromal cells from the toxic effects of currently available antivirals such as 5-trifluoromethyl-2'-deoxyuridine and 5-iodo-2'-deoxyuridine. The selective protection of DNA, RNA, and protein synthesis will also be studied in rabbit corneas and in keratocyte cultures. The knowledge gained from these studies on the metabolism of antivirals will be applied in studies designed to develop alternative forms of chemotherapy to treat keratitis produced by mutant viruses and to determine the role of viral metabolism in pathogenesis. The proposed research will also investigate the effects of combined antiviral/corticosteroid therapy on macromolecular synthesis in corneal cells undergoing wound healing responses because clinical situations often arise when both compounds are administered simultaneously. The long-term goal of our research is to develop less toxic and more effective forms of antiviral therapy.